Antibiotics of cephalosporin type are known to be highly active against a variety of gram-positive and gram-negative bacteria with high safety for mammals, so that they have been used widely and effectively for the therapeutic treatments of infectious diseases in mammals including man. In recent years, many researches have been directed to develop new classes of cephalosporin antibiotics of such a type that the cephalosporin compounds contain an aminothiazolylacetyl group as the acyl group in the 7-acylamino side chain on the cephem nucleus because they have been considered as being particularly attractive in view of their high anti-bacterial activity and stability to .beta.-lactamase.
It is known that a family of such cephem compounds having a phenylglycylamino group on the 7-position and a relatively small functional group on the 3-position of the cephem compound, e.g. hydrogen atom, a halogen atom, or a methyl group, an alkoxy group, alkoxymethyl group or alkylthio group, as represented by cephalexin, generally possess a high absorption capacity through digestive tracts of patient upon oral administration. However, the antibacterial activity of such cephem compounds orally administered is always much inferior, against gram-negative bacteria, inter alia, against gram-negative bacteria capable of producing .beta.-lactamase, to that of such cephalosporin compounds which are normally given to patient by injective administration.
Recently, on the other hand, there have been developed as oral administration drugs new cephalosporin compounds of which the 7-acylamino group contains an aminothiazole group, which are presented in the form of an ester derivative of the 4-carboxyl group, and of which the ester-forming group is easily clearable with the action of esterase existing in the digestive tracts. These caphalosporin antibiotics of the aminothiazole type can exhibit higher antibacterial activities against gram-negative bacteria than that of cephalexin, but unfortunately have such drawbacks that their anti-bacterial activities against gram-positive bacteria are rather lowered and that their absorption through digestive tracts of patient upon oral administration is still not satisfactorily high.
We, the present inventors, have proceeded with our investigations with a view to solving the problems discussed above and now succeeded in synthesizing a a new class of cephalosporin derivatives represented by a general formula (I) given below and we have found that they have a broad antibacterial spectrum and a high absorption capacity upon oral administration, in combination.